As is known in the art, thermal coupling for heating or cooling, in practice, takes place either through flowing media, such as air or liquid, through heat radiation, or through mechanical contact.
When using flowing media, the heat flow from a first body to a second body can be controlled by changing the quantity of flowing medium. However, to accomplish this purpose, a relatively expensive pump structure or thermosiphon structure is required. In addition, it is very difficult to control the high temperatures of the flowing medium through the structure.
The application of heat radiation is very limited as the low heat transport in the heat radiation procedure of thermal coupling functions only in the case of relatively high temperature differences. Moreover, a regulated control of the heat flow is very difficult to realize.
Mechanical contact leads to the lowest heat losses and devices based on mechanical contact are easily constructed. However, the disadvantage of a mechanical contact type of thermal coupling is the loss of the possibility of controlling the heat flow. This is because it is only possible to change the heat flow through a mechanical change of the contact.
A thermal coupling between two parts is very often necessary in which the maximum temperature of one of the two bodies is not to be exceeded, for instance in the construction of technical measuring instruments and apparatus, and also in industrial installations. The coupling can take place either through mechanical contact or through flowing media. In the case of mechanical contact, the problem of constant heat conduction exists even with high temperatures whereby one of the two parts involved in the coupling can be damaged due to its limited temperature stability. A decrease of the thermal contact is required in applications of this type when exceeding a given temperature limit. However, a decrease of the thermal contact is practically only possible through mechanical separation of the two connecting surfaces.
One application of such thermal coupling is the regulation of the temperature of a body. If this body is thermally well insulated, the regulation functions very well at high temperatures due to the heat radiation. If the body is to be rapidly cooled again, a good heat conduction to a cooling body is required. However, a permanent heat conduction to the cooling body would prevent heating to high temperatures.
Another example of an application of such thermal coupling where a maximum temperature limit cannot be exceeded is the use of thermoelectric elements, for instance Peltier elements, for heating and cooling of apparatuses and installation parts. Another possible application is for using these Peltier elements for the direct conversion of electrical energy from heat.
A significant disadvantage of commercially available Peltier elements is that the temperature range is limited at the high end. This high end limit is determined primarily through the usable alloys of the Peltier elements and through the soldering material used most often, soldering tin. Thus, the temperature range which can be reached with Peltier elements is limited to a maximum of about 250.degree. C. Additional heating to a higher temperature leads to the destruction of the Peltier elements.